xfs: garbage collect old cowextsz reservations

Trim CoW reservations made on behalf of a cowextsz hint if they get too
old or we run low on quota, so long as we don't have dirty data awaiting
writeback or directio operations in progress.

Garbage collection of the cowextsize extents are kept separate from
prealloc extent reaping because setting the CoW prealloc lifetime to a
(much) higher value than the regular prealloc extent lifetime has been
useful for combatting CoW fragmentation on VM hosts where the VMs
experience bursty write behaviors and we can keep the utilization ratios
low enough that we don't start to run out of space.  IOWs, it benefits
us to keep the CoW fork reservations around for as long as we can unless
we run out of blocks or hit inode reclaim.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>

15 files changed, 287 insertions, 32 deletions

diff --git a/fs/xfs/xfs_bmap_util.c b/fs/xfs/xfs_bmap_util.c
index 4a807f0..eacd4c2 100644
--- a/fs/xfs/xfs_bmap_util.c
+++ b/fs/xfs/xfs_bmap_util.c
@@ -1891,6 +1891,8 @@ xfs_swap_extents(
 		cowfp = ip->i_cowfp;
 		ip->i_cowfp = tip->i_cowfp;
 		tip->i_cowfp = cowfp;
+		xfs_inode_set_cowblocks_tag(ip);
+		xfs_inode_set_cowblocks_tag(tip);
 	}
 
 	xfs_trans_log_inode(tp, ip,  src_log_flags);
diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
index 07f951d..0726df8 100644
--- a/fs/xfs/xfs_file.c
+++ b/fs/xfs/xfs_file.c
@@ -782,6 +782,9 @@ write_retry:
 		enospc = xfs_inode_free_quota_eofblocks(ip);
 		if (enospc)
 			goto write_retry;
+		enospc = xfs_inode_free_quota_cowblocks(ip);
+		if (enospc)
+			goto write_retry;
 	} else if (ret == -ENOSPC && !enospc) {
 		struct xfs_eofblocks eofb = {0};
 
diff --git a/fs/xfs/xfs_globals.c b/fs/xfs/xfs_globals.c
index 4d41b24..687a4b0 100644
--- a/fs/xfs/xfs_globals.c
+++ b/fs/xfs/xfs_globals.c
@@ -21,8 +21,8 @@
 /*
  * Tunable XFS parameters.  xfs_params is required even when CONFIG_SYSCTL=n,
  * other XFS code uses these values.  Times are measured in centisecs (i.e.
- * 100ths of a second) with the exception of eofb_timer, which is measured in
- * seconds.
+ * 100ths of a second) with the exception of eofb_timer and cowb_timer, which
+ * are measured in seconds.
  */
 xfs_param_t xfs_params = {
 			  /*	MIN		DFLT		MAX	*/
@@ -42,6 +42,7 @@ xfs_param_t xfs_params = {
 	.inherit_nodfrg	= {	0,		1,		1	},
 	.fstrm_timer	= {	1,		30*100,		3600*100},
 	.eofb_timer	= {	1,		300,		3600*24},
+	.cowb_timer	= {	1,		1800,		3600*24},
 };
 
 struct xfs_globals xfs_globals = {
diff --git a/fs/xfs/xfs_icache.c b/fs/xfs/xfs_icache.c
index 2d3de02..14796b7 100644
--- a/fs/xfs/xfs_icache.c
+++ b/fs/xfs/xfs_icache.c
@@ -33,6 +33,7 @@
 #include "xfs_bmap_util.h"
 #include "xfs_dquot_item.h"
 #include "xfs_dquot.h"
+#include "xfs_reflink.h"
 
 #include <linux/kthread.h>
 #include <linux/freezer.h>
@@ -792,6 +793,33 @@ xfs_eofblocks_worker(
 	xfs_queue_eofblocks(mp);
 }
 
+/*
+ * Background scanning to trim preallocated CoW space. This is queued
+ * based on the 'speculative_cow_prealloc_lifetime' tunable (5m by default).
+ * (We'll just piggyback on the post-EOF prealloc space workqueue.)
+ */
+STATIC void
+xfs_queue_cowblocks(
+	struct xfs_mount *mp)
+{
+	rcu_read_lock();
+	if (radix_tree_tagged(&mp->m_perag_tree, XFS_ICI_COWBLOCKS_TAG))
+		queue_delayed_work(mp->m_eofblocks_workqueue,
+				   &mp->m_cowblocks_work,
+				   msecs_to_jiffies(xfs_cowb_secs * 1000));
+	rcu_read_unlock();
+}
+
+void
+xfs_cowblocks_worker(
+	struct work_struct *work)
+{
+	struct xfs_mount *mp = container_of(to_delayed_work(work),
+				struct xfs_mount, m_cowblocks_work);
+	xfs_icache_free_cowblocks(mp, NULL);
+	xfs_queue_cowblocks(mp);
+}
+
 int
 xfs_inode_ag_iterator(
 	struct xfs_mount	*mp,
@@ -1348,18 +1376,30 @@ xfs_inode_free_eofblocks(
 	return ret;
 }
 
-int
-xfs_icache_free_eofblocks(
+static int
+__xfs_icache_free_eofblocks(
 	struct xfs_mount	*mp,
-	struct xfs_eofblocks	*eofb)
+	struct xfs_eofblocks	*eofb,
+	int			(*execute)(struct xfs_inode *ip, int flags,
+					   void *args),
+	int			tag)
 {
 	int flags = SYNC_TRYLOCK;
 
 	if (eofb && (eofb->eof_flags & XFS_EOF_FLAGS_SYNC))
 		flags = SYNC_WAIT;
 
-	return xfs_inode_ag_iterator_tag(mp, xfs_inode_free_eofblocks, flags,
-					 eofb, XFS_ICI_EOFBLOCKS_TAG);
+	return xfs_inode_ag_iterator_tag(mp, execute, flags,
+					 eofb, tag);
+}
+
+int
+xfs_icache_free_eofblocks(
+	struct xfs_mount	*mp,
+	struct xfs_eofblocks	*eofb)
+{
+	return __xfs_icache_free_eofblocks(mp, eofb, xfs_inode_free_eofblocks,
+			XFS_ICI_EOFBLOCKS_TAG);
 }
 
 /*
@@ -1368,9 +1408,11 @@ xfs_icache_free_eofblocks(
  * failure. We make a best effort by including each quota under low free space
  * conditions (less than 1% free space) in the scan.
  */
-int
-xfs_inode_free_quota_eofblocks(
-	struct xfs_inode *ip)
+static int
+__xfs_inode_free_quota_eofblocks(
+	struct xfs_inode	*ip,
+	int			(*execute)(struct xfs_mount *mp,
+					   struct xfs_eofblocks	*eofb))
 {
 	int scan = 0;
 	struct xfs_eofblocks eofb = {0};
@@ -1406,14 +1448,25 @@ xfs_inode_free_quota_eofblocks(
 	}
 
 	if (scan)
-		xfs_icache_free_eofblocks(ip->i_mount, &eofb);
+		execute(ip->i_mount, &eofb);
 
 	return scan;
 }
 
-void
-xfs_inode_set_eofblocks_tag(
-	xfs_inode_t	*ip)
+int
+xfs_inode_free_quota_eofblocks(
+	struct xfs_inode *ip)
+{
+	return __xfs_inode_free_quota_eofblocks(ip, xfs_icache_free_eofblocks);
+}
+
+static void
+__xfs_inode_set_eofblocks_tag(
+	xfs_inode_t	*ip,
+	void		(*execute)(struct xfs_mount *mp),
+	void		(*set_tp)(struct xfs_mount *mp, xfs_agnumber_t agno,
+				  int error, unsigned long caller_ip),
+	int		tag)
 {
 	struct xfs_mount *mp = ip->i_mount;
 	struct xfs_perag *pag;
@@ -1431,26 +1484,22 @@ xfs_inode_set_eofblocks_tag(
 
 	pag = xfs_perag_get(mp, XFS_INO_TO_AGNO(mp, ip->i_ino));
 	spin_lock(&pag->pag_ici_lock);
-	trace_xfs_inode_set_eofblocks_tag(ip);
 
-	tagged = radix_tree_tagged(&pag->pag_ici_root,
-				   XFS_ICI_EOFBLOCKS_TAG);
+	tagged = radix_tree_tagged(&pag->pag_ici_root, tag);
 	radix_tree_tag_set(&pag->pag_ici_root,
-			   XFS_INO_TO_AGINO(ip->i_mount, ip->i_ino),
-			   XFS_ICI_EOFBLOCKS_TAG);
+			   XFS_INO_TO_AGINO(ip->i_mount, ip->i_ino), tag);
 	if (!tagged) {
 		/* propagate the eofblocks tag up into the perag radix tree */
 		spin_lock(&ip->i_mount->m_perag_lock);
 		radix_tree_tag_set(&ip->i_mount->m_perag_tree,
 				   XFS_INO_TO_AGNO(ip->i_mount, ip->i_ino),
-				   XFS_ICI_EOFBLOCKS_TAG);
+				   tag);
 		spin_unlock(&ip->i_mount->m_perag_lock);
 
 		/* kick off background trimming */
-		xfs_queue_eofblocks(ip->i_mount);
+		execute(ip->i_mount);
 
-		trace_xfs_perag_set_eofblocks(ip->i_mount, pag->pag_agno,
-					      -1, _RET_IP_);
+		set_tp(ip->i_mount, pag->pag_agno, -1, _RET_IP_);
 	}
 
 	spin_unlock(&pag->pag_ici_lock);
@@ -1458,9 +1507,22 @@ xfs_inode_set_eofblocks_tag(
 }
 
 void
-xfs_inode_clear_eofblocks_tag(
+xfs_inode_set_eofblocks_tag(
 	xfs_inode_t	*ip)
 {
+	trace_xfs_inode_set_eofblocks_tag(ip);
+	return __xfs_inode_set_eofblocks_tag(ip, xfs_queue_eofblocks,
+			trace_xfs_perag_set_eofblocks,
+			XFS_ICI_EOFBLOCKS_TAG);
+}
+
+static void
+__xfs_inode_clear_eofblocks_tag(
+	xfs_inode_t	*ip,
+	void		(*clear_tp)(struct xfs_mount *mp, xfs_agnumber_t agno,
+				    int error, unsigned long caller_ip),
+	int		tag)
+{
 	struct xfs_mount *mp = ip->i_mount;
 	struct xfs_perag *pag;
 
@@ -1470,23 +1532,141 @@ xfs_inode_clear_eofblocks_tag(
 
 	pag = xfs_perag_get(mp, XFS_INO_TO_AGNO(mp, ip->i_ino));
 	spin_lock(&pag->pag_ici_lock);
-	trace_xfs_inode_clear_eofblocks_tag(ip);
 
 	radix_tree_tag_clear(&pag->pag_ici_root,
-			     XFS_INO_TO_AGINO(ip->i_mount, ip->i_ino),
-			     XFS_ICI_EOFBLOCKS_TAG);
-	if (!radix_tree_tagged(&pag->pag_ici_root, XFS_ICI_EOFBLOCKS_TAG)) {
+			     XFS_INO_TO_AGINO(ip->i_mount, ip->i_ino), tag);
+	if (!radix_tree_tagged(&pag->pag_ici_root, tag)) {
 		/* clear the eofblocks tag from the perag radix tree */
 		spin_lock(&ip->i_mount->m_perag_lock);
 		radix_tree_tag_clear(&ip->i_mount->m_perag_tree,
 				     XFS_INO_TO_AGNO(ip->i_mount, ip->i_ino),
-				     XFS_ICI_EOFBLOCKS_TAG);
+				     tag);
 		spin_unlock(&ip->i_mount->m_perag_lock);
-		trace_xfs_perag_clear_eofblocks(ip->i_mount, pag->pag_agno,
-					       -1, _RET_IP_);
+		clear_tp(ip->i_mount, pag->pag_agno, -1, _RET_IP_);
 	}
 
 	spin_unlock(&pag->pag_ici_lock);
 	xfs_perag_put(pag);
 }
 
+void
+xfs_inode_clear_eofblocks_tag(
+	xfs_inode_t	*ip)
+{
+	trace_xfs_inode_clear_eofblocks_tag(ip);
+	return __xfs_inode_clear_eofblocks_tag(ip,
+			trace_xfs_perag_clear_eofblocks, XFS_ICI_EOFBLOCKS_TAG);
+}
+
+/*
+ * Automatic CoW Reservation Freeing
+ *
+ * These functions automatically garbage collect leftover CoW reservations
+ * that were made on behalf of a cowextsize hint when we start to run out
+ * of quota or when the reservations sit around for too long.  If the file
+ * has dirty pages or is undergoing writeback, its CoW reservations will
+ * be retained.
+ *
+ * The actual garbage collection piggybacks off the same code that runs
+ * the speculative EOF preallocation garbage collector.
+ */
+STATIC int
+xfs_inode_free_cowblocks(
+	struct xfs_inode	*ip,
+	int			flags,
+	void			*args)
+{
+	int ret;
+	struct xfs_eofblocks *eofb = args;
+	bool need_iolock = true;
+	int match;
+
+	ASSERT(!eofb || (eofb && eofb->eof_scan_owner != 0));
+
+	if (!xfs_reflink_has_real_cow_blocks(ip)) {
+		trace_xfs_inode_free_cowblocks_invalid(ip);
+		xfs_inode_clear_cowblocks_tag(ip);
+		return 0;
+	}
+
+	/*
+	 * If the mapping is dirty or under writeback we cannot touch the
+	 * CoW fork.  Leave it alone if we're in the midst of a directio.
+	 */
+	if (mapping_tagged(VFS_I(ip)->i_mapping, PAGECACHE_TAG_DIRTY) ||
+	    mapping_tagged(VFS_I(ip)->i_mapping, PAGECACHE_TAG_WRITEBACK) ||
+	    atomic_read(&VFS_I(ip)->i_dio_count))
+		return 0;
+
+	if (eofb) {
+		if (eofb->eof_flags & XFS_EOF_FLAGS_UNION)
+			match = xfs_inode_match_id_union(ip, eofb);
+		else
+			match = xfs_inode_match_id(ip, eofb);
+		if (!match)
+			return 0;
+
+		/* skip the inode if the file size is too small */
+		if (eofb->eof_flags & XFS_EOF_FLAGS_MINFILESIZE &&
+		    XFS_ISIZE(ip) < eofb->eof_min_file_size)
+			return 0;
+
+		/*
+		 * A scan owner implies we already hold the iolock. Skip it in
+		 * xfs_free_eofblocks() to avoid deadlock. This also eliminates
+		 * the possibility of EAGAIN being returned.
+		 */
+		if (eofb->eof_scan_owner == ip->i_ino)
+			need_iolock = false;
+	}
+
+	/* Free the CoW blocks */
+	if (need_iolock) {
+		xfs_ilock(ip, XFS_IOLOCK_EXCL);
+		xfs_ilock(ip, XFS_MMAPLOCK_EXCL);
+	}
+
+	ret = xfs_reflink_cancel_cow_range(ip, 0, NULLFILEOFF);
+
+	if (need_iolock) {
+		xfs_iunlock(ip, XFS_MMAPLOCK_EXCL);
+		xfs_iunlock(ip, XFS_IOLOCK_EXCL);
+	}
+
+	return ret;
+}
+
+int
+xfs_icache_free_cowblocks(
+	struct xfs_mount	*mp,
+	struct xfs_eofblocks	*eofb)
+{
+	return __xfs_icache_free_eofblocks(mp, eofb, xfs_inode_free_cowblocks,
+			XFS_ICI_COWBLOCKS_TAG);
+}
+
+int
+xfs_inode_free_quota_cowblocks(
+	struct xfs_inode *ip)
+{
+	return __xfs_inode_free_quota_eofblocks(ip, xfs_icache_free_cowblocks);
+}
+
+void
+xfs_inode_set_cowblocks_tag(
+	xfs_inode_t	*ip)
+{
+	trace_xfs_inode_set_eofblocks_tag(ip);
+	return __xfs_inode_set_eofblocks_tag(ip, xfs_queue_cowblocks,
+			trace_xfs_perag_set_eofblocks,
+			XFS_ICI_COWBLOCKS_TAG);
+}
+
+void
+xfs_inode_clear_cowblocks_tag(
+	xfs_inode_t	*ip)
+{
+	trace_xfs_inode_clear_eofblocks_tag(ip);
+	return __xfs_inode_clear_eofblocks_tag(ip,
+			trace_xfs_perag_clear_eofblocks, XFS_ICI_COWBLOCKS_TAG);
+}
diff --git a/fs/xfs/xfs_icache.h b/fs/xfs/xfs_icache.h
index 05bac99..a1e02f4 100644
--- a/fs/xfs/xfs_icache.h
+++ b/fs/xfs/xfs_icache.h
@@ -40,6 +40,7 @@ struct xfs_eofblocks {
 					   in xfs_inode_ag_iterator */
 #define XFS_ICI_RECLAIM_TAG	0	/* inode is to be reclaimed */
 #define XFS_ICI_EOFBLOCKS_TAG	1	/* inode has blocks beyond EOF */
+#define XFS_ICI_COWBLOCKS_TAG	2	/* inode can have cow blocks to gc */
 
 /*
  * Flags for xfs_iget()
@@ -70,6 +71,12 @@ int xfs_inode_free_quota_eofblocks(struct xfs_inode *ip);
 void xfs_eofblocks_worker(struct work_struct *);
 void xfs_queue_eofblocks(struct xfs_mount *);
 
+void xfs_inode_set_cowblocks_tag(struct xfs_inode *ip);
+void xfs_inode_clear_cowblocks_tag(struct xfs_inode *ip);
+int xfs_icache_free_cowblocks(struct xfs_mount *, struct xfs_eofblocks *);
+int xfs_inode_free_quota_cowblocks(struct xfs_inode *ip);
+void xfs_cowblocks_worker(struct work_struct *);
+
 int xfs_inode_ag_iterator(struct xfs_mount *mp,
 	int (*execute)(struct xfs_inode *ip, int flags, void *args),
 	int flags, void *args);
diff --git a/fs/xfs/xfs_inode.c b/fs/xfs/xfs_inode.c
index 09640bd..89e6441 100644
--- a/fs/xfs/xfs_inode.c
+++ b/fs/xfs/xfs_inode.c
@@ -1629,8 +1629,10 @@ xfs_itruncate_extents(
 	/*
 	 * Clear the reflink flag if we truncated everything.
 	 */
-	if (ip->i_d.di_nblocks == 0 && xfs_is_reflink_inode(ip))
+	if (ip->i_d.di_nblocks == 0 && xfs_is_reflink_inode(ip)) {
 		ip->i_d.di_flags2 &= ~XFS_DIFLAG2_REFLINK;
+		xfs_inode_clear_cowblocks_tag(ip);
+	}
 
 	/*
 	 * Always re-log the inode so that our permanent transaction can keep
diff --git a/fs/xfs/xfs_linux.h b/fs/xfs/xfs_linux.h
index b8d64d5..68640fb 100644
--- a/fs/xfs/xfs_linux.h
+++ b/fs/xfs/xfs_linux.h
@@ -116,6 +116,7 @@ typedef __u32			xfs_nlink_t;
 #define xfs_inherit_nodefrag	xfs_params.inherit_nodfrg.val
 #define xfs_fstrm_centisecs	xfs_params.fstrm_timer.val
 #define xfs_eofb_secs		xfs_params.eofb_timer.val
+#define xfs_cowb_secs		xfs_params.cowb_timer.val
 
 #define current_cpu()		(raw_smp_processor_id())
 #define current_pid()		(current->pid)
diff --git a/fs/xfs/xfs_mount.c b/fs/xfs/xfs_mount.c
index 40fedc0..fc78739 100644
--- a/fs/xfs/xfs_mount.c
+++ b/fs/xfs/xfs_mount.c
@@ -1049,6 +1049,7 @@ xfs_unmountfs(
 	int			error;
 
 	cancel_delayed_work_sync(&mp->m_eofblocks_work);
+	cancel_delayed_work_sync(&mp->m_cowblocks_work);
 
 	xfs_fs_unreserve_ag_blocks(mp);
 	xfs_qm_unmount_quotas(mp);
diff --git a/fs/xfs/xfs_mount.h b/fs/xfs/xfs_mount.h
index 0be14a7..819b80b 100644
--- a/fs/xfs/xfs_mount.h
+++ b/fs/xfs/xfs_mount.h
@@ -164,6 +164,8 @@ typedef struct xfs_mount {
 	struct delayed_work	m_reclaim_work;	/* background inode reclaim */
 	struct delayed_work	m_eofblocks_work; /* background eof blocks
 						     trimming */
+	struct delayed_work	m_cowblocks_work; /* background cow blocks
+						     trimming */
 	bool			m_update_sb;	/* sb needs update in mount */
 	int64_t			m_low_space[XFS_LOWSP_MAX];
 						/* low free space thresholds */
diff --git a/fs/xfs/xfs_reflink.c b/fs/xfs/xfs_reflink.c
index e92ccd3..685c419 100644
--- a/fs/xfs/xfs_reflink.c
+++ b/fs/xfs/xfs_reflink.c
@@ -304,6 +304,9 @@ retry:
 		goto out_unlock;
 	}
 
+	if (end_fsb != orig_end_fsb)
+		xfs_inode_set_cowblocks_tag(ip);
+
 	trace_xfs_reflink_cow_alloc(ip, &got);
 done:
 	*offset_fsb = end_fsb;
@@ -1562,6 +1565,7 @@ next:
 	/* Clear the inode flag. */
 	trace_xfs_reflink_unset_inode_flag(ip);
 	ip->i_d.di_flags2 &= ~XFS_DIFLAG2_REFLINK;
+	xfs_inode_clear_cowblocks_tag(ip);
 	xfs_trans_ijoin(*tpp, ip, 0);
 	xfs_trans_log_inode(*tpp, ip, XFS_ILOG_CORE);
 
@@ -1662,3 +1666,37 @@ out:
 	trace_xfs_reflink_unshare_error(ip, error, _RET_IP_);
 	return error;
 }
+
+/*
+ * Does this inode have any real CoW reservations?
+ */
+bool
+xfs_reflink_has_real_cow_blocks(
+	struct xfs_inode		*ip)
+{
+	struct xfs_bmbt_irec		irec;
+	struct xfs_ifork		*ifp;
+	struct xfs_bmbt_rec_host	*gotp;
+	xfs_extnum_t			idx;
+
+	if (!xfs_is_reflink_inode(ip))
+		return false;
+
+	/* Go find the old extent in the CoW fork. */
+	ifp = XFS_IFORK_PTR(ip, XFS_COW_FORK);
+	gotp = xfs_iext_bno_to_ext(ifp, 0, &idx);
+	while (gotp) {
+		xfs_bmbt_get_all(gotp, &irec);
+
+		if (!isnullstartblock(irec.br_startblock))
+			return true;
+
+		/* Roll on... */
+		idx++;
+		if (idx >= ifp->if_bytes / sizeof(xfs_bmbt_rec_t))
+			break;
+		gotp = xfs_iext_get_ext(ifp, idx);
+	}
+
+	return false;
+}
diff --git a/fs/xfs/xfs_reflink.h b/fs/xfs/xfs_reflink.h
index bade5a6..5dc3c8a 100644
--- a/fs/xfs/xfs_reflink.h
+++ b/fs/xfs/xfs_reflink.h
@@ -53,4 +53,6 @@ extern int xfs_reflink_clear_inode_flag(struct xfs_inode *ip,
 extern int xfs_reflink_unshare(struct xfs_inode *ip, xfs_off_t offset,
 		xfs_off_t len);
 
+extern bool xfs_reflink_has_real_cow_blocks(struct xfs_inode *ip);
+
 #endif /* __XFS_REFLINK_H */
diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c
index 90a8fd7..15b9fcd 100644
--- a/fs/xfs/xfs_super.c
+++ b/fs/xfs/xfs_super.c
@@ -1531,6 +1531,7 @@ xfs_fs_fill_super(
 	atomic_set(&mp->m_active_trans, 0);
 	INIT_DELAYED_WORK(&mp->m_reclaim_work, xfs_reclaim_worker);
 	INIT_DELAYED_WORK(&mp->m_eofblocks_work, xfs_eofblocks_worker);
+	INIT_DELAYED_WORK(&mp->m_cowblocks_work, xfs_cowblocks_worker);
 	mp->m_kobj.kobject.kset = xfs_kset;
 
 	mp->m_super = sb;
diff --git a/fs/xfs/xfs_sysctl.c b/fs/xfs/xfs_sysctl.c
index aed74d3..afe1f66 100644
--- a/fs/xfs/xfs_sysctl.c
+++ b/fs/xfs/xfs_sysctl.c
@@ -184,6 +184,15 @@ static struct ctl_table xfs_table[] = {
 		.extra1		= &xfs_params.eofb_timer.min,
 		.extra2		= &xfs_params.eofb_timer.max,
 	},
+	{
+		.procname	= "speculative_cow_prealloc_lifetime",
+		.data		= &xfs_params.cowb_timer.val,
+		.maxlen		= sizeof(int),
+		.mode		= 0644,
+		.proc_handler	= proc_dointvec_minmax,
+		.extra1		= &xfs_params.cowb_timer.min,
+		.extra2		= &xfs_params.cowb_timer.max,
+	},
 	/* please keep this the last entry */
 #ifdef CONFIG_PROC_FS
 	{
diff --git a/fs/xfs/xfs_sysctl.h b/fs/xfs/xfs_sysctl.h
index ffef453..984a349 100644
--- a/fs/xfs/xfs_sysctl.h
+++ b/fs/xfs/xfs_sysctl.h
@@ -48,6 +48,7 @@ typedef struct xfs_param {
 	xfs_sysctl_val_t inherit_nodfrg;/* Inherit the "nodefrag" inode flag. */
 	xfs_sysctl_val_t fstrm_timer;	/* Filestream dir-AG assoc'n timeout. */
 	xfs_sysctl_val_t eofb_timer;	/* Interval between eofb scan wakeups */
+	xfs_sysctl_val_t cowb_timer;	/* Interval between cowb scan wakeups */
 } xfs_param_t;
 
 /*
diff --git a/fs/xfs/xfs_trace.h b/fs/xfs/xfs_trace.h
index 5c10b12..263dab1 100644
--- a/fs/xfs/xfs_trace.h
+++ b/fs/xfs/xfs_trace.h
@@ -136,6 +136,8 @@ DEFINE_PERAG_REF_EVENT(xfs_perag_set_reclaim);
 DEFINE_PERAG_REF_EVENT(xfs_perag_clear_reclaim);
 DEFINE_PERAG_REF_EVENT(xfs_perag_set_eofblocks);
 DEFINE_PERAG_REF_EVENT(xfs_perag_clear_eofblocks);
+DEFINE_PERAG_REF_EVENT(xfs_perag_set_cowblocks);
+DEFINE_PERAG_REF_EVENT(xfs_perag_clear_cowblocks);
 
 DECLARE_EVENT_CLASS(xfs_ag_class,
 	TP_PROTO(struct xfs_mount *mp, xfs_agnumber_t agno),
@@ -687,6 +689,9 @@ DEFINE_INODE_EVENT(xfs_dquot_dqdetach);
 DEFINE_INODE_EVENT(xfs_inode_set_eofblocks_tag);
 DEFINE_INODE_EVENT(xfs_inode_clear_eofblocks_tag);
 DEFINE_INODE_EVENT(xfs_inode_free_eofblocks_invalid);
+DEFINE_INODE_EVENT(xfs_inode_set_cowblocks_tag);
+DEFINE_INODE_EVENT(xfs_inode_clear_cowblocks_tag);
+DEFINE_INODE_EVENT(xfs_inode_free_cowblocks_invalid);
 
 DEFINE_INODE_EVENT(xfs_filemap_fault);
 DEFINE_INODE_EVENT(xfs_filemap_pmd_fault);